The overtraining syndrome describes the condition in which an athlete suffers from various complications resulting from overtraining. These typically include overuse injuries, mood disturbances and blood chemistry changes. Although there is no gold-standard criterion for diagnosing this syndrome, the best current indicators include prolonged fatigue, impaired athletic performance and psychological changes. This article aims to provide some insights into the physiology of overtraining, with emphasis on its cardiovascular consequences. Impaired cardiac function may occur after prolonged exercise, and is documented by depressed left ventricular function and decreased myocardial oxygen ventilation rates. Electrocardiographic abnormalities which may be seen in overtraining are T wave inversions, ST segment depressions and various arrhythmias. Well-conditioned athletes may also manifest the same abnormalities as a result of physiological cardiac hypertrophy. Electrocardiography and two-dimensional echocardiography should form an integral part of the screening performed by any sports medicine department overseeing the training of athletes.